CMC and Cloud Point of Nonionic Ethoxylated Surfactants: Experimental Data and Molecular Thermodynamics

High Resolution Image Download MS PowerPoint Slide Surface tension and cloud point experiments were performed for a series of ethoxylated surfactants ( C 12 E 7, C 12 E 12, and C 12 E 23 ), and the results were compared with predictions from a molecular thermodynamic model and molecular dynamics simulations. The critical micelle concentration (CMC) was determined by surface tension measurements using a regularization function, with probability envelopes constructed taking into account the experimental uncertainty. The observed CMC values exhibited a systematic dependence on the degree of ethoxylation, with C 12 E 7 presenting the largest variability. This behavior is associated with its lower CMC, which required measurements at lower concentrations, thereby increasing the relative errors in this range. Cloud point measurements using Crystal16 confirmed a double cloud point for C 12 E 7, characteristic of surfactants with short EO chains, while C 12 E 12 and C 12 E 23 exhibited single transitions. The thermodynamic model reproduced the experimental data of cloud point with good accuracy for C 12 E 23 but underestimated cloud points for C 12 E 12, highlighting the need for refined parametrization of EO–solvent interactions in the presence of salt. Complementary molecular dynamics simulations captured the amphiphilic behavior of C 12 E 7, reproducing the reduction in surface tension with increasing surfactant concentration. Collectively, these findings demonstrate that integrating experiments, thermodynamic modeling, and molecular simulations provides a robust framework for understanding micellization and phase behavior of ethoxylated surfactants.